Adaptive grouping of parameters for enhanced coding efficiency

ABSTRACT

The present invention is based on the finding that parameters including a first set of parameters of a representation of a first portion of an original signal and including a second set of parameters of a representation of a second portion of the original signal can be efficiently encoded, when the parameters are arranged in a first sequence of tuples and in a second sequence of tuples, wherein the first sequence of tuples comprises tuples of parameters having two parameters from a single portion of the original signal and wherein the second sequence of tuples comprises tuples of parameters having one parameter from the first portion and one parameter from the second portion of the original signal. An efficient encoding can be achieved using a bit estimator to estimate the number of necessary bits to encode the first and the second sequence of tuples, wherein only the sequence of tuples is encoded, that results in the lower number of bits.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit under 35 U.S.C. 119(e) of U.S.provisional application No. 60/670,993, filed Apr. 13, 2005. The priorapplication is herewith incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to lossless encoding of parameters, and,in particular, to the generation and use of an encoding rule forefficient compression of parameters.

BACKGROUND OF THE INVENTION AND PRIOR ART

In recent times, the multi-channel audio reproduction technique isbecoming more and more important. This may be due to the fact that audiocompression/encoding techniques such as the well-known mp3 techniquehave made it possible to distribute audio records via the Internet orother transmission channels having a limited bandwidth. The mp3 codingtechnique has become so famous because of the fact that it allowsdistribution of all the records in a stereo format, i.e., a digitalrepresentation of the audio record including a first or left stereochannel and a second or right stereo channel.

Nevertheless, there are basic shortcomings of conventional two-channelsound systems. Therefore, the surround technique has been developed. Arecommended multi-channel-surround representation includes, in additionto the two stereo channels L and R, an additional center channel C andtwo surround channels Ls, Rs. This reference sound format is alsoreferred to as three/two-stereo, which means three front channels andtwo surround channels. Generally, five transmission channels arerequired. In a playback environment, at least five speakers at fivedecent places are needed to get an optimum sweet spot in a certaindistance of the five well-placed loudspeakers.

Several techniques are known in the art for reducing the amount of datarequired for transmission of a multi-channel audio signal. Suchtechniques are called joint stereo techniques. To this end, reference ismade to FIG. 9, which shows a joint stereo device 60. This device can bea device implementing e.g. intensity stereo (IS) or binaural cue coding(BCC). Such a device generally receives—as an input—at least twochannels (CH1, CH2, . . . CHn), and outputs at least a single carrierchannel and parametric data. The parametric data are defined such that,in a decoder, an approximation of an original channel (CH1, CH2, . . .CHn) can be calculated.

Normally, the carrier channel will include subband samples, spectralcoefficients, time domain samples etc., which provide a comparativelyfine representation of the underlying signal, while the parametric datado not include such samples of spectral coefficients but include controlparameters for controlling a certain reconstruction algorithm such asweighting by multiplication, time shifting, frequency shifting, phaseshifting, etc. The parametric data, therefore, include only acomparatively coarse representation of the signal or the associatedchannel. Stated in numbers, the amount of data required by a carrierchannel will be in the range of 60-70 kbit/s, while the amount of datarequired by parametric side information for one channel will typicallybe in the range of 1,5-2,5 kbit/s. An example for parametric data arethe well-known scale factors, intensity stereo information or binauralcue parameters as will be described below.

The BCC Technique is for example described in the AES convention paper5574, “Binaural Cue Coding applied to Stereo and Multi-Channel AudioCompression”, C. Faller, F. Baumgarte, May 2002, Munich, in the IEEEWASPAA Paper “Efficient representation of spatial audio using perceptualparametrization”, October 2001, Mohonk, N.Y., in “Binaural cue codingapplied to audio compression with flexible rendering”, C. Faller and F.Baumgarte, AES 113^(th) Convention, Los Angeles, Preprint 5686, October2002 and in “Binaural cue coding—Part II: Schemes and applications”, C.Faller and F. Baumgarte, IEEE Trans. on Speech and Audio Proc., volumelevel. 11, no. 6, November 2003.

In BCC encoding, a number of audio input channels are converted to aspectral representation using a DFT (Discrete Fourier Transform) basedtransform with overlapping windows. The resulting uniform spectrum isdivided into non-overlapping partitions. Each partition approximatelyhas a bandwidth proportional to the equivalent rectangular bandwidth(ERB). The BCC parameters are then estimated between two channels foreach partition. These BCC parameters are normally given for each channelwith respect to a reference channel and are furthermore quantized. Thetransmitted parameters are finally calculated in accordance withprescribed formulas (encoded), which may also depend on the specificpartitions of the signal to be processed.

A number of BCC parameters do exist. The ICLD parameter, for example,describes the difference (ratio) of the energies contained in 2 comparedchannels. The ICC parameter (inter-channel coherence/correlation)describes the correlation between the two channels, which can beunderstood as the similarity of the waveforms of the two channels. TheICTD parameter (inter-channel time difference) describes a global timeshift between the 2 channels whereas the IPD parameter (inter-channelphase difference) describes the same with respect to the phases of thesignals.

One should be aware that, in a frame-wise processing of an audio signal,the BCC analysis is also performed frame-wise, i.e. time-varying, andalso frequency-wise. This means that, for each spectral band, the BCCparameters are individually obtained. This further means that, in case aaudio filter bank decomposes the input signal into for example 32 bandpass signals, a BCC analysis block obtains a set of BCC parameters foreach of the 32 bands.

A related technique, also known as parametric stereo, is described in J.Breebaart, S. van de Par, A. Kohlrausch, E. Schuijers, “High-QualityParametric Spatial Audio Coding at Low Bitrates”, AES 116th Convention,Berlin, Preprint 6072, May 2004, and E. Schuijers, J. Breebaart, H.Purnhagen, J. Engdegard, “Low Complexity Parametric Stereo Coding”, AES116th Convention, Berlin, Preprint 6073, May 2004.

Summarizing, recent approaches for parametric coding of multi-channelaudio signals (“Spatial Audio Coding”, “Binaural Cue Coding” (BCC) etc.)represent a multi-channel audio signal by means of a downmix signal(could be monophonic or comprise several channels) and parametric sideinformation (“spatial cues”) characterizing its perceived spatial soundstage. It is desirable to keep the rate of side information as low aspossible in order to minimize overhead information and leave as much ofthe available transmission capacity for the coding of the downmixsignals.

One way to keep the bit rate of the side information low is tolosslessly encode the side information of a spatial audio scheme byapplying, for example, entropy coding algorithms to the sideinformation.

Lossless coding has been extensively applied in general audio coding inorder to ensure an optimally compact representation for quantizedspectral coefficients and other side information. Examples forappropriate encoding schemes and methods are given within the ISO/IECstandards MPEG1 part 3, MPEG2 part 7 and MPEG4 part 3.

These standards and, for example also the IEEE paper “Noiseless Codingof Quantized Spectral Coefficients in MPEG-2 Advanced Audio Coding”, S.R. Quackenbush, J. D. Johnston, IEEE WASPAA, Mohonk, N.Y., October 1997describes state of the art techniques that include the followingmeasures to losslessly encode quantized parameters:

-   -   Multi-dimensional Huffman Coding of quantized spectral        coefficients    -   Using a common (multi-dimensional) Huffman Codebook for sets of        coefficients    -   Coding the value either as a hole or coding sign information and        magnitude information separately (i.e. have only Huffman        codebook entries for a given absolute value which reduces the        necessary codebook size, “signed” vs. “unsigned” codebooks)    -   Using alternative codebooks of different largest absolute values        (LAVs), i.e. different maximum absolute values within the        parameters to be encoded    -   Using alternative codebooks of different statistical        distribution for each LAV    -   Transmitting the choice of Huffman codebook as side information        to the decoder    -   Using “sections” to define the range of application of each        selected Huffman codebook    -   Differential encoding of scalefactors over frequency and        subsequent Huffman coding of the result

Another technique for the lossless encoding of coarsely quantized valuesinto a single PCM code is proposed within the MPEG1 audio standard(called grouping within the standard and used for layer 2). This isexplained in more detail within the standard ISO/IEC 11172-3:93.

The publication “Binaural cue coding—Part II: Schemes and applications”,C. Faller and F. Baumgarte, IEEE Trans. on Speech and Audio Proc.,volume level. 11, no. 6, November 2003 gives some information on codingof BCC parameters. It is proposed, that quantized ICLD parameters aredifferentially encoded

-   -   over frequency and the result is subsequently Huffman encoded        (with a one-dimensional Huffman code)    -   over time and the result is subsequently Huffman encoded (with a        one-dimensional Huffman code),        and that finally, the more efficient variant is selected as the        representation of an original audio signal.

As mentioned above, it has been proposed to optimize compressionperformance by applying differential coding over frequency and,alternatively, over time and select the more efficient variant. Theselected variant is then signaled to a decoder via some sideinformation.

There has been quite some effort made to reduce the size of a downmixaudio channel and the corresponding side information. Nonetheless theachievable bit rates are still too high to allow for every possibleapplication. For example, streaming of audio and video content to mobilephones requires the least possible bit rates and therefore a moreefficient encoding of the content.

SUMMARY OF THE INVENTION

It is the object of the present invention to provide an improved codingconcept achieving a lossless compression of parameter values with higherefficiency.

In accordance with the first aspect of the present invention, thisobject is achieved by a compression unit for compression of parameters,the parameters including a first set of parameters including arepresentation of a first portion of an original signal, the parametersfurther including a second set of parameters including a representationof a second portion of the original signal, the second portionneighboring the first portion, comprising: a supplier for supplying afirst tuple and a second tuple, each tuple having at least twoparameters, the first tuple having two parameters from the first set ofparameters and the second tuple having one parameter from the first setof parameters and one parameter from the second set of parameters; a bitestimator for estimating a number of bits necessary to encode the setsof parameters using a first sequence of tuples including the first tupleand to encode the sets of parameters using a second sequence of tuplesincluding the second tuple, based on an encoding rule; and a providerfor providing encoded blocks, the provider being operative to providethe encoded blocks using the sequence of tuples resulting in a lowernumber of bits, and for providing a sequence indication indicating thesequence of tuples from which the encoded blocks are derived.

In accordance with the second aspect of the present invention, thisobject is achieved by a decoder for decoding encoded blocks ofparameters, the parameters including a first set of parameters includinga representation of a first portion of an original signal, theparameters further including a second set of parameters including arepresentation of a second portion of the original signal, the secondportion neighboring the first portion, and for processing a sequenceindication, comprising: a decompressor, the decompressor being operativeto decompress, using a decoding rule depending on an encoding rule usedfor encoding sequences of tuples, an encoded block of parameters toderive a sequence of tuples of parameters, each tuple having at leasttwo parameters; and a frame builder for receiving the sequenceindication, the sequence indication indicating a used sequence of tuplesfrom a number of different sequences underlying the encoded block, andfor building the sets of parameters using the information of the usedsequence of tuples.

In accordance with the third aspect of the present invention, thisobject is achieved by a method for compression of parameters, theparameters including a first set of parameters including arepresentation of a first portion of an original signal, the parametersfurther including a second set of parameters including a representationof a second portion of the original signal, the second portionneighboring the first portion.

In accordance with the fourth aspect of the present invention, thisobject is achieved by a computer program implementing the above method,when running on a computer.

In accordance with the fifth aspect of the present invention, thisobject is achieved by a method for decoding encoded blocks ofparameters, the parameters including a first set of parameters includinga representation of a first portion of an original signal, theparameters further including a second set of parameters including arepresentation of a second portion of the original signal, the secondportion neighboring the first portion, and for processing a sequenceindication.

In accordance with the sixth aspect of the present invention, thisobject is achieved by a computer program implementing the above method,when running on a computer.

In accordance with the seventh aspect of the present invention, thisobject is achieved by a compressed representation of parameters, theparameters including a first set of parameters including arepresentation of a first portion of an original signal, the parametersfurther including a second set of parameters including a representationof a second portion of the original signal, the second portionneighboring the first portion of the original signal, comprising: anencoded block of parameters representing a used sequence of tuples; anda sequence indication indicating the used sequence of tuples of a firstor a second sequence underlying the encoded block of parameters, wherethe first sequence includes a first tuple having two parameters from thefirst set of parameters and where the second sequence includes a secondtuple having one parameter from the first set of parameters and oneparameter from the second set of parameters.

The present invention is based on the finding that parameters includinga first set of parameters of a representation of a first portion of anoriginal signal and including a second set of parameters of arepresentation of a second portion of the original signal can beefficiently encoded, when the parameters are arranged in a firstsequence of tuples and in a second sequence of tuples, wherein the firstsequence of tuples comprises tuples of parameters having two parametersfrom a single portion of the original signal and wherein the secondsequence of tuples comprises tuples of parameters having one parameterfrom the first portion and one parameter from the second portion of theoriginal signal. An efficient encoding can be achieved using a bitestimator to estimate the number of necessary bits to encode the firstand the second sequence of tuples, wherein only the sequence of tuplesis encoded, that results in the lower number of bits.

The basic principle therefore is, that one rearranges the parameters tobe encoded, for example in time and in frequency, and finally uses theone arrangement (sequence of tuples) of the parameters for thecompression, that results in the lower number of bits for the compressedparameters.

In one embodiment of the present invention, two sets of spectralparameters, describing the spectral representation of two consecutivetime portions of an original signal are adaptively grouped in pairs oftwo parameters to enhance the coding efficiency. Therefore, on the onehand a sequence of tuples is generated using tuples of parametersconsisting of two neighboring frequency parameters from the same timeportion. On the other hand, a second sequence of tuples is generatedusing tuples, that are built using a first parameter from the first timeportion and the corresponding parameter from the second time portion ofthe original signal. Then, both sequences of tuples are encoded using atwo-dimensional Huffman code. The two encoded sequences of tuples arecompared in their sizes and the tuple resulting in the lower number ofbits is finally selected to be transmitted. The information, which kindof tuples has been used to build the encoded data is transmitted to adecoder as additional side information.

One advantage of the previously described inventive encoder is, that dueto the grouping of parameters into tuples consisting of two parameters,a two-dimensional Huffman code can be applied for the compression, whichgenerally results in a lower bit rate.

A second advantage is, that the adaptive grouping, i.e. the concept todynamically decide between two possible grouping strategies during theencoding process, yields a further decrease in the bit rate of the sideinformation.

Deciding between the two grouping strategies only once for a set of twoconsecutive frames additionally reduces the amount of required sideinformation, since the indication, which grouping strategy has been usedduring the encoding, has to be transmitted only once for a set of twocomplete consecutive time frames.

In a further embodiment of the present invention an inventivecompression unit additionally comprises a differential encoder, thatdifferentially encodes the parameters either in time or in frequencyprior to the adaptive grouping. That differential encoding together withthe adaptive grouping and an appropriate Huffman codebook furtherreduces the size of the side information to be transmitted. The twodifferential encoding possibilities together with the two groupingstrategies result in a total number of four possible combinations,further increasing the probability of finding an encoding rule, thatresults in a low side information bit rate.

In a further embodiment of the present invention, the inventive conceptis used for a decompression unit, allowing to decode encoded blocks ofparameters and to rebuild the original frames based on a sideinformation signaling the grouping scheme underlying the encoded blocksof parameters. In an advantageous modification the inventive decoderalso allows the decoding of data that has not been adaptively grouped,therefore a compatibility of the inventive decoder with existingequipment can be achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention are subsequentlydescribed by referring to the enclosed drawings, wherein:

FIG. 1 shows an inventive compression unit;

FIG. 2 shows two possibilities of adaptively grouping parameters;

FIG. 3 shows some additional possibilities of adaptively groupingparameters;

FIG. 4 shows differential encoding schemes;

FIG. 5 shows an inventive decoder;

FIG. 6 shows a prior art multi-channel encoder.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows an inventive compression unit 90, comprising a supplier100, a bit estimator 102 and a provider 104.

The supplier 100 supplies a first sequence of tuples 106 a and a secondsequence of tuples 106 b at two data outputs. The provider 104 receivesthe tuples 106 a and 106 b on two of his data inputs 108 a and 108 b.The bit estimator receives the two tuples on his data inputs 110 a and110 b.

The bit estimator 102 estimates the number of bits that result fromapplying an encoding rule to the two tuples 106 a and 106 b. The bitestimator 102 chooses the tuple resulting in the lower number of bitsand signals via a signaling output 112 a, whether the tuple 106 a or 106b will result in the lower number of bits.

Based on the decision of the bit estimator 102, the tuple resulting inthe lower number of bits is finally encoded into encoded blocks 118,that are provided via output 120 a of the provider 104, wherein theprovider further signals a sequence indication at his signaling line 120b, indicating what original sequence of tuples (106 a or 106 b) wasencoded to derive the encoded blocks 118.

In an alternative embodiment, the same functionality can be achieved,when the dashed connections 122 a and 122 b between the supplier 100 andthe provider 104 are omitted. In this alternative scenario the bitestimator 102 would encode the sequence of tuples 106 a and 106 b, andwould transfer two different encoded blocks 124 a and 124 b to theprovider 104, where the provider additionally signals from which of theoriginal sequences of tuples 106 a and 106 b the encoded blocks 124 aand 124 b are derived. To this end, the signaling output 112 a of thebit estimator 102 can be used or the signaling can be derived by theprovider 104 implicitly.

In this alternative embodiment the provider 104 would simply forward theencoded block with the lower number of bits to its output 120 a,additionally providing the sequence indication.

FIG. 2 shows an example of two adaptive grouping schemes that are usedto derive a sequence of tuples to be encoded. To explain the principleof the inventive adaptive grouping, four subsequent time frames 130 a to130 d of an original signal are shown, wherein each of the frames ishaving a set of five spectral parameters 132 a to 132 e.

According to the present invention, the spectral parameters of twoconsecutive frames are grouped either in frequency, as illustrated bythe tuples 134 a and 134 b or in time, as illustrated by the tuples 136a and 136 b to build the sequences of tuples. The grouping in timeresults in a first sequence of tuples 138, whereas the grouping infrequency results in the second sequence of tuples 140.

The sequences of tuples 138 and 140 are encoded using for example aHuffman codebook, resulting into two different sequences of code words142 and 144. According to the present invention, the sequence of codewords requiring the fewer number of bits, is finally transmitted to adecoder, that has to additionally receive a sequence indication,signaling whether time grouping or frequency grouping is underlying thesequence of code words. As can be seen in FIG. 2, for the shown exampleof adaptive grouping of pairs of parameters (2-dimensional), thesequence indication can consist of only one single bit.

FIG. 3 shows some alternative grouping strategies that can be used toimplement the inventive adaptive grouping, allowing for Huffman codeswith dimensions bigger than 2.

FIG. 3 shows a grouping strategy for a two-dimensional Huffman code 146a, for a three-dimensional Huffman code 146 b and a for afour-dimensional Huffman code 146 c. For each of the strategies twoconsecutive time frames are illustrated, wherein the parametersbelonging to the same tuple are represented by the same capital letters.

In the case of the two-dimensional Huffman code the grouping is done asalready illustrated in FIG. 2, building two-dimensional tuples infrequency 148 a and in time 148 b. In case of building tuples consistingof three parameters, the frequency tuples 158 a are such, that threeneighboring frequency parameters within one frame are grouped togetherto form a tuple. The time tuples 150 b can be built such, that twoneighboring parameters from one frame are combined with one parameterfrom the other frame, as is shown in FIG. 3.

Four-dimensional time grouped tuples 152 a are built corresponding tothe other time tuples by grouping four neighboring parameters of oneframe into one tuple. The time grouping tuples 152 b are built such,that two neighboring parameters of one frame are combined with twoneighboring parameters of the other frame, wherein the parameter pairsof the single frames are describing the same spectral property of thetwo consecutive time frames.

Allowing different grouping schemes, as illustrated in FIG. 3, one cansignificantly reduce the bit rate of the side information, for exampleif one uses a variety of predefined Huffman codebooks of differentdimensions, the dimension of the grouping can be varied within theencoding process such, that the representation resulting in the lowestbit rate can be used at any time within the encoding process.

FIG. 4 shows, how an inventive compression unit, that additionallycomprises a differential encoder, can be used to further decrease theside information, by applying some differential encoding before theHuffman encoding process.

To illustrate the differential encoding in time and frequency or in timeand frequency, the same absolute representation of parameters 160 thatwas already shown in FIG. 2, is used as a basis for the variousdifferential encoding steps. The first possibility is to differentiallyencode the parameters of the absolute representation 160 in frequency,resulting in the differentially encoded parameters 162. As can be seenin FIG. 4, to differentially encode the absolute representation 160, thefirst parameter of each frame is left unchanged, whereas the secondparameter is replaced by the difference of the second parameter and thefirst parameter of the absolute representation 160. The other parameterswithin the differentially encoded representation are built following thesame rule.

Another possibility is the differential coding in time, yielding therepresentation 164. This representation is built by leaving the completefirst frame unchanged, whereas the parameters of the following framesare replaced by the difference of the parameter of the absoluterepresentation and the same parameter of the previous frame, as can beseen in FIG. 4.

A third possibility is to first encode differentially in frequency,followed by a differential encoding in time or vice versa, bothresulting in the same encoded representation 166, that is differentiallyencoded in time and frequency.

It is to be noted, that one has the chance to use those four differentrepresentations of the original signal as input to the adaptivegrouping. Having a look at the different representations 160 to 166 ofthe given example of parameters, one can clearly see how thedifferential encoding has impact on the transmitted rate of sideinformation. Looking at the absolute representation 160, one recognizes,that neither a grouping in time nor in frequency would result in tupleshaving the same content. Therefore no appropriate Huffman codebook isconstructable, that would assign the shortest code words to the tuplesoccurring most.

The case is different looking at the differentially in frequency encodedrepresentation 162, where one could construct a Huffman codebook thatonly needs to have four entries to cover the full representation, andwhere either the tuple (1, 1) or the tuple (2, 2) would be assigned thecode word with minimum length, to achieve a compact side information.

The advantage is less obvious in the representation being differentiallyencoded in time 164. Nonetheless one can gain also here, grouping infrequency and making use of the numerous tuples (5, 5) and (10, 10).

For the representation that is differentially encoded in time and infrequency 166, one would even achieve a further reduction of the sideinformation bit rate than in the representation 162, since a grouping intime would result in a high multiplicity of the tuple (1, 0), asindicated in the figure, allowing to construct a Huffman codebook, thatwould assign the shortest code word to the previous tuple.

As can be clearly seen in FIG. 4, the high flexibility of the inventiveconcept making use of adaptive grouping and of differential encodingallows to choose the strategy that fits the original audio signal most,thus allowing to keep the side information bit rate low.

To summarize, in one preferred embodiment the quantized parameter valuesare first differentially encoded over time (variant 1) anddifferentially over frequency (variant 2). The resulting parameters canthen be grouped adaptively over time (variant a) and frequency (variantb). As a result, four combinations are available (1 a, 1 b, 2 a, 2 b)from which the best is selected and signaled to the decoder. This couldbe done by a 2 bit information only, representing the variants 1 a, 1 b,2 a, 2 b by, for example, the bit combination 00, 01, 10, 11.

FIG. 5 shows a decoder according to the current invention, to decodeencoded blocks of parameters, wherein the block of parameters includes afirst frame having a set of first spectral parameters and a second framehaving a set of second spectral parameters.

The decoder 200 comprises a decompressor 202 and a frame builder 204.The decompressor receives on an input an encoded block of parameters206. The decompressor derives, using a decoding rule, a sequence oftuples of parameters 208 from the encoded block of parameters 206. Thissequence of tuples of parameters 208 is input into the frame builder204.

The frame builder additionally receives a sequence indication 210,indicating what sequence of tuples have been used by the encoder tobuild the encoded block of parameters.

The frame builder 204 then reorders the sequence of tuples 208 steeredby the sequence indication 210 to reconstruct the first frame 112 a andthe second frame 112 b from the sequence of tuples of parameters 208.

Preferred embodiments of the present invention described above achieve afurther enhancement of the coding efficiency by introducing adaptivegrouping of values to be coded using a multi-dimensional Huffman code.As an example, both, two-dimensional grouping of values over frequencycan be done as well as two-dimensional grouping of values over time. Theencoding scheme would then do both types of encoding and choose the moreadvantageous one (i.e. the variant which requires less bits). Thisdecision is signaled to the decoder via side information.

In further examples, as illustrated in FIG. 3, it is also possible tobuild higher-dimensional Huffman codes, applying different groupingstrategies to build the tuples. The given examples show groupingstrategies that build the tuples by grouping together parameters fromtwo consecutive frames only. It is also possible to do the groupingusing parameters from three or more consecutive frames, doing thegrouping in a straightforward way.

In a modification of the inventive encoder, it is also possible tocombine the differential grouping and the differential encodingstrategies with the use of different Huffman codebooks to derive theshortest possible representation of the side information. This couldfurther reduce the side information bit rate of an encoded audio signalat the cost of having additional side information parameters, signalingthe Huffman codebook used for the encoding.

The described preferred embodiments of the present invention show theinventive concept for examples, where the grouping strategy does notchange within two consecutive time frames. In a modification of thepresent invention it is of course also possible, to have multiplechanges between the grouping in time and in frequency within a set oftwo frames, which would imply that the sequence indication is alsosupplied within the frames, to signal the change of grouping strategy.

In the given examples, the parameters are differentially encoded beforebeing Huffman encoded. Of course every other lossless encoding rule isalso possible prior to the Huffman encoding of the parameters, the aimof the encoding being to derive as much tuples with the same content aspossible.

There are four different possible parameter representations given inFIG. 4, namely the absolute representation, the differentialrepresentation in frequency, the differential representation in time andthe differential representation in time and frequency. To choose betweenfour representations, the side information signaling whichrepresentation has been used, has to be at least two bits in size, asindicated in FIG. 4. To balance the win of a possible efficiency gain ofthe coding versus the additional spectral representation indication, onecould of course also decide to principally allow only two possiblerepresentations, reducing the spectral representation indication to thelength of a single bit.

As an example of an inventive decoder, FIG. 5 shows a decoder 200 thatreceives in addition to the encoded block of parameters 206 some sideinformation. The side information steering the frame builder 204 onlycomprises a sequence indication 210 in the given example. A decoderaccording to the present invention can of course process any other sideinformation required, especially a spectral representation indication,indicating the spectral representation that has been used to encodeoriginal frames.

Depending on certain implementation requirements of the inventivemethods, the inventive methods can be implemented in hardware or insoftware. The implementation can be performed using a digital storagemedium, in particular a disk, DVD or a CD having electronically readablecontrol signals stored thereon, which cooperate with a programmablecomputer system such that the inventive methods are performed.Generally, the present invention is, therefore, a computer programproduct with a program code stored on a machine-readable carrier, theprogram code being operative for performing the inventive methods whenthe computer program product runs on a computer. In other words, theinventive methods are, therefore, a computer program having a programcode for performing at least one of the inventive methods when thecomputer program runs on a computer.

While the foregoing has been particularly shown and described withreference to particular embodiments thereof, it will be understood bythose skilled in the art that various other changes in the form anddetails may be made without departing from the spirit and scope thereof.It is to be understood that various changes may be made in adapting todifferent embodiments without departing from the broader conceptsdisclosed herein and comprehended by the claims that follow.

1. Compression unit for compression of parameters, the parametersincluding a first set of parameters including a representation of afirst portion of an original signal, the parameters further including asecond set of parameters including a representation of a second portionof the original signal, the second portion neighboring the firstportion, comprising: a supplier for supplying a first tuple and a secondtuple, each tuple having at least two parameters, the first tuple havingtwo parameters from the first set of parameters and the second tuplehaving one parameter from the first set of parameters and one parameterfrom the second set of parameters; a bit estimator for estimating anumber of bits necessary to encode the sets of parameters using a firstsequence of tuples including the first tuple and to encode the sets ofparameters using a second sequence of tuples including the second tuple,based on an encoding rule; and a provider for providing encoded blocks,the provider being operative to provide the encoded blocks using thesequence of tuples resulting in a lower number of bits, and forproviding a sequence indication indicating the sequence of tuples fromwhich the encoded blocks are derived.
 2. Compression unit in accordancewith claim 1 in which the first and the second set of parameters areincluding a spectral representation of the first and the second portionof the original signal as representation.
 3. Compression unit inaccordance with claim 1, in which the first portion and the secondportion of the original signal are neighbored in time or in space. 4.Compression unit in accordance with claim 1, in which the first set ofparameters includes a representation of a first frame of an originalaudio or video signal and in which the second set of parameters includesa representation of a second frame of the original audio or videosignal.
 5. Compression unit in accordance with claim 1, in which thesupplier is operative to supply the first tuple and all remaining tuplesof the first sequence of tuples using only tuples having parameters fromone single set of parameters, and to supply the first tuple and allremaining tuples of the second sequence of tuples using only tupleshaving at least one parameter from the first set of parameters and atleast one parameter from the second set of parameters; and in which theprovider is operative to provide a single sequence indication for oneencoded block.
 6. Compression unit in accordance with claim 1, in whichthe supplier is operative to supply the first tuple consisting of twoparameters from a single set of parameters, the two parameters beingneighbored parameters within the representation of the original signal;and the second tuple consisting of a first parameter from the first setof parameters and a second parameter from the second set of parameters,the first and the second parameter describing the same property of theoriginal signal within the representation.
 7. Compression unit inaccordance with claim 1, in which the supplier is operative to supplythe first tuple consisting of an integer multiple of two parameters froma single set of parameters, the parameters being neighbored parameterswithin the representation of the original signal; and the second tupleconsisting of an two or more parameters from the first set ofparameters, the parameters being neighbored within the representation ofthe original signal and of the same number of parameters from the secondset of parameters, the parameters being neighbored within therepresentation of the original signal, the parameters from the first andthe second set of parameters describing the same properties of theoriginal signal within the representation.
 8. Compression unit inaccordance with claim 1, in which the supplier is operative to supplythe first tuple consisting of an odd number of neighboring parameters ofthe representation of the original signal from one set of parameters;and the second tuple consisting of a majority of neighboring parametersof the representation of the original signal from one set of parametersand of a minority of neighboring parameters of the representation of theoriginal signal from the other set of parameters, wherein the majorityof parameters is alternatingly taken from the first and from the secondset of parameters for consecutive tuples of the second sequence oftuples.
 9. Compression unit in accordance with claim 1, in which the bitestimator is operative to encode, using the encoding rule, the firstsequence of tuples to derive a first encoded block and to encode thesecond sequence of tuples to derive a second encoded block, and toestimate the necessary number of bits by counting the bits of the firstand of the second encoded block; and in which the provider is operativeto forward the first or the second encoded block, choosing the blockwith the lower number of bits.
 10. Compression unit in accordance withclaim 1, in which the bit estimator is operative to estimate the bitsnecessary to encode the sequences of tuples according to the encodingrule; and in which the provider is operative to encode the sequence oftuples providing the encoded block with the lower number of bits. 11.Compression unit in accordance with claim 1, in which the sets ofparameters are comprising a parametric representation of a video signalor of an audio signal.
 12. Compression unit in accordance with claim 1,in which the encoding rule is such, that encoding tuples having the samelength but different parameters can result in codewords of differentlength.
 13. Compression unit in accordance with claim 1, in which theparameters include BCC parameters describing a spatial interrelationbetween a first and a second original audio channel and in which the BCCparameters are chosen from the following list of BCC parameters:interchannel coherence/correlation (ICC) interchannel level difference(ICLD) interchannel time difference (ICTD) interchannel phase difference(IPD).
 14. Compression unit in accordance with claim 1, furthercomprising a differential encoder for processing the original signalsuch, that the first set of parameters and the second set of parametersinclude a difference representation, the difference being a differencein time, in frequency or in time and in frequency.
 15. Compression unitin accordance with claim 14, in which the supplier is operative tosupply a first group of tuples and a second group of tuples, the tupleswithin the groups of tuples having parameters from one of the followingrepresentations: a differential representation in time, a differentialrepresentation in frequency, a differential representation in time andin frequency, and an absolute representation, wherein the first group oftuples is having tuples with two parameters from the first set ofparameters and wherein the second group of tuples is having oneparameter from the first and one parameter from the second set ofparameters; and in which the bit estimator is operative to estimate thenumber of bits necessary to encode sequences of tuples for at leasteight sequences of tuples, each sequence having one of the tuples of thegroups of tuples; and in which the provider is operative to signal, inaddition to the sequence indication, a representation indicationindicating the representation resulting in the lower number of bits. 16.Compression unit in accordance with claim 15, in which the provider isoperational to signal the sequence indication and the representationindication using a binary data word having at least three bits. 17.Compression unit in accordance with claim 1, in which the encoding ruleis such, that each tuple has associated therewith a single code word ofa group of different code words.
 18. Compression unit in accordance withclaim 1, in which the encoding rule includes a Huffman codebook.
 19. Adecoder for decoding encoded blocks of parameters, the parametersincluding a first set of parameters including a representation of afirst portion of an original signal, the parameters further including asecond set of parameters including a representation of a second portionof the original signal, the second portion neighboring the firstportion, and for processing a sequence indication, comprising: adecompressor, the decompressor being operative to decompress, using adecoding rule depending on an encoding rule used for encoding sequencesof tuples, an encoded block of parameters to derive a sequence of tuplesof parameters, each tuple having at least two parameters; and a framebuilder for receiving the sequence indication, the sequence indicationindicating a used sequence of tuples from a number of differentsequences underlying the encoded block, and for building the sets ofparameters using the information of the used sequence of tuples. 20.Decoder in accordance with claim 19 in which the first and the secondsets of parameters are including a spectral representation of the firstand the second portion of the original signal as representation. 21.Decoder in accordance with claim 19, in which the first portion and thesecond portion of the original signal are neighbored in time or inspace.
 22. Decoder in accordance with claim 19, in which the first setof parameters includes a representation of a first frame of an originalaudio or video signal and in which the second set of parameters includesa representation of a second frame of the original audio or videosignal.
 23. Decoder in accordance with claim 19, in which the framebuilder is operative to receive a single sequence indication for oneencoded block of parameters, and to build the sets of parameters byusing a sequence of tuples comprising only tuples of the type indicatedby the sequence indication.
 24. Decoder in accordance with claim 19, inwhich the frame builder is operative to build sets of parameterscomprising a parametric representation of a video signal or of an audiosignal.
 25. Decoder in accordance with claim 19, in which the framebuilder is operative to build sets of parameters comprising BCCparameters describing a spatial interrelation between a first and asecond audio channel and in which the BCC parameters are chosen form thefollowing list of BCC parameters: interchannel coherence/correlation(ICC) interchannel level difference (ICLD) interchannel time difference(ICTD) interchannel phase difference (IPD).
 26. Decoder in accordancewith claim 19, further comprising a differential decoder for receiving arepresentation indication and for processing the sets of parameterssuch, that the parameters are derived from a difference spectralrepresentation, the difference being a difference in time, in frequencyor in time and in frequency, wherein the differential decoder isoperative to process the first and the second set of parametersdepending on the representation indication.
 27. Decoder in accordancewith claim 26, in which the frame builder and the differential decoderare operative to receive a sequence indication and a representationindication as a binary data word having at least three bits.
 28. Decoderin accordance with claim 19, in which the decoding rule is such, thateach code word within the encoded block of parameters has associatedtherewith a single tuple of a group of different tuples.
 29. A methodfor compression of parameters, the parameters including a first set ofparameters including a representation of a first portion of an originalsignal, the parameters further including a second set of parametersincluding a representation of a second portion of the original signal,the second portion neighboring the first portion, the method comprising:supplying a first tuple and a second tuple, each tuple having at leasttwo parameters, the first tuple having two parameters from the first setof parameters and the second tuple having one parameter from the firstset of parameters and one parameter from the second set of parameters;estimating a number of bits necessary to encode the sets of parametersusing a first sequence of tuples including the first tuple and to encodethe frames using a second sequence of tuples including the second tuple,based on an encoding rule; providing encoded blocks using the sequenceof tuples resulting in a lower number of bits; and providing a sequenceindication indicating the sequence of tuples from which the encodedblocks are derived.
 30. A method for decoding encoded blocks ofparameters, the parameters including a first set of parameters includinga representation of a first portion of an original signal, theparameters further including a second set of parameters including arepresentation of a second portion of the original signal, the secondportion neighboring the first portion, and for processing a sequenceindication, the method comprising: decompressing, using a decoding ruledepending on an encoding rule used for encoding sequences of tuples, theencoded block of parameters to derive a sequence of tuples ofparameters, each tuple having at least two parameters; receiving thesequence indication indicating a used sequence of tuples from a numberof different sequences underlying the encoded block; and building thesets of parameters using the information of the used sequence of tuples.31. Computer program having a program code for performing, when runningon a computer, a method for compression of parameters, the parametersincluding a first set of parameters including a representation of afirst portion of an original signal, the parameters further including asecond set of parameters including a representation of a second portionof the original signal, the second portion neighboring the firstportion, the method comprising: supplying a first tuple and a secondtuple, each tuple having at least two parameters, the first tuple havingtwo parameters from the first set of parameters and the second tuplehaving one parameter from the first set of parameters and one parameterfrom the second set of parameters; estimating a number of bits necessaryto encode the sets of parameters using a first sequence of tuplesincluding the first tuple and to encode the frames using a secondsequence of tuples including the second tuple, based on an encodingrule; providing encoded blocks using the sequence of tuples resulting ina lower number of bits; and providing a sequence indication indicatingthe sequence of tuples from which the encoded blocks are derived. 32.Computer program having a program code for performing, when running on acomputer, a method for decoding encoded blocks of parameters, theparameters including a first set of parameters including arepresentation of a first portion of an original signal, the parametersfurther including a second set of parameters including a representationof a second portion of the original signal, the second portionneighboring the first portion, and for processing a sequence indication,the method comprising: decompressing, using a decoding rule depending onan encoding rule used for encoding sequences of tuples, the encodedblock of parameters to derive a sequence of tuples of parameters, eachtuple having at least two parameters; receiving the sequence indication,the sequence indication indicating a used sequence of tuples from anumber of different sequences underlying the encoded block; and buildingthe sets of parameters using the information of the used sequence oftuples.
 33. Compressed representation of parameters, the parametersincluding a first set of parameters including a representation of afirst portion of an original signal, the parameters further including asecond set of parameters including a representation of a second portionof the original signal, the second portion neighboring the first portionof the original signal, comprising: an encoded block of parametersrepresenting a used sequence of tuples; and a sequence indicationindicating the used sequence of tuples of a first or a second sequenceunderlying the encoded block of parameters, where the first sequenceincludes a first tuple having two parameters from the first set ofparameters and where the second sequence includes a second tuple havingone parameter from the first set of parameters and one parameter fromthe second set of parameters.
 34. Compressed representation ofparameters in accordance with claim 33, which is stored on a computerreadable media.